This invention relates to a diffraction grating, an optical pickup device, and an optical disc apparatus.
As a background art of this technical field, Japanese Patent Laid-open Application (JP-A) No. 2005-122869 describes, in Problem to be Solved by the Invention, that influences by eccentricity of a disc-shaped recording medium etc. are reduced, so that the quality of a tracking error signal is intended to be improved, and also describes, in Means for Solving the Problem that an optical pickup device, as solving means, is provided with a diffraction grating 10 that makes possible recording or reproduction of an information signal for two or more kinds of disc-shaped recording media 100 used for respective different working wavelengths and has plural areas each of which divides each of laser lights of different wavelengths emitted from emitting elements 9 into a main optical beam, a pair of first sub optical beams, and a pair of second sub optical beams; moreover, a distance D between spot centers of the first sub optical beams and spot centers of the second sub optical beams formed separately on a recording surface of any one of the two or more kinds of disc-shaped recording media is made substantially equal to (2n−1)×P/2, where n denotes a nonnegative integer and P denotes a track pitch of any one of the two or more kinds of disc-shaped recording media.
As another background art of this technical field, there is an article of the Nikkei Electronics, p. 47, Oct. 25, 2004.